1. Field of the Invention
The present invention relates generally to fluid filled vibration damping devices exhibiting damping effect on the basis of flows of the non-compressible fluid sealed therein, and more particularly to a fluid filled vibration damping device of novel construction, which may be usable as an engine mount or other mounts for use in automotive vehicles.
2. Description of the Related Art
A fluid filled vibration damping device is known as one type of a vibration-damping coupling or mount adapted to be installed between two members of a vibration systems so as to elastically connect or support the two members in a vibration-damping fashion. A typical fluid filled vibration-damping device includes, as shown in JP-A-2001-59540 for example, a rubber elastic body elastically connecting a first and second mounting member fixable to one and the other member of the vibration system, respectively, a pressure receiving chamber partially defined by the rubber elastic body and filled with a non compressible fluid, an equilibrium chamber partially defined by a flexible layer and filled with the non-compressible fluid, and an orifice passage for permitting a fluid communication between the pressure-receiving chamber and the equilibrium chamber. Upon application of a vibrational load between the first and second mounting members, a fluid pressure in the pressure receiving chamber varies due to the elastic deformation of the elastic body, while a change in volume of the equilibrium chamber is permitted due to elastic displacement or deformation of the flexible layer, whereby the fluid is forced to flow through the orifice passage between the pressure receiving chamber and the equilibrium chamber. Such a conventional fluid filled vibration damping device is able to exhibit excellent vibration damping effect on the basis of resonance or flows of the fluid through the orifice passage, which effect is so superior that a vibration damping device simply relying on a rubber elastic body cannot achieve it. For the above-described advantage, the conventional fluid filled vibration damping device has been attempted to be used as an engine mount, a body mount, or other mounts for automotive vehicles, for example.
In the conventional vibration damping device, the flexible layer is generally formed of a thin rubber elastic layer. In order to provide a sufficient amount of fluid flows through the orifice passage upon application of vibration, and in order to realize an excellent damping performance of the device, important is to permit sufficient amount of volumetric change in the equilibrium chamber by sufficiently increasing a permissible amount of distending deformation of the flexible layer.
However, if the permissible amount of distending deformation of the flexible layer is excessively large, the flexible layer excessively distending outwardly would be brought into contact with a bracket or other members, when these members are disposed in the vicinity of the flexible layer. This may possibly cause a problem of deterioration in durability of the flexible layer.
To enhance the durability of the flexible layer, it may be proposed to increase the wall thickness of the overall flexible layer. However, this measure makes it difficult for the flexible layer to permit a sufficient permissible amount of distending deformation thereof, possibly leading to decrease in the amount of fluid flows through the orifice passage, whereby the damping performance with the help of the orifice passage is considerably decreased.
Further, in order to enhance durability of the flexible layer, it may be proposed to partially increase the wall thickness of the flexible layer, at an interference area where the flexible layer is brought into contact with the other member(s). In this measure, although the flexible layer has its wall thickness enlarged in the interference area, the interference between the flexible layer and the other member(s) is not avoidable, and the interference area of the flexible layer is finally brought into contact with the other member(s). Conversely, this may cause a relatively large impact noise in comparison with the case where the flexible layer has no thick walled portion. Therefore, the conventionally proposed measures have not been appropriate to solve the aforesaid conventionally experienced problems.